1. Prior Art
Classically, a basic and natural arrangement for carrier aggregation aims at managing independently each channel using several independent PHY layers.
A basic arrangement is for example illustrated by FIG. 1A in the case of two aggregated channels.
Considering the example of FIG. 1A, the basic arrangement implements a chain of modules for processing each channel. Each chain of modules comprises for example a first module (111, 112) comprising a receiving antenna and radio frequency (RF) means for processing the received analog signal comprising for example at least a low-noise amplifier LNA, and an analog-to-digital converter ADC, one or a plurality of filters and gain amplifiers, a second module (121, 122) comprising a waveshaping filter, a third module (131, 132) implementing a Fast Fourier Transform FFT managing the OFDM transmission, a fourth module (141, 142) for the channel estimation, which computes the channel information over the channel bandwidth, a fifth module (151, 152) comprising an equalizer, which extracts the useful carriers out of the N available at the FFT output and compensates for the channel distortion using the channel estimations and a sixth module (161, 162) comprising a turbo decoder.
In this example, the part of the chain comprising these six modules corresponds to the process that is implemented for each channel in the PHY layers and can be called the “front end” and delivers decoded data.
Note that in the following the terminology “front end” refers to the part of the chain of each channel that is upstream to the aggregation point. Consequently, the terminology “back-end” will refers to the part of the “aggregated” chain that is downstream to the aggregation point.
FIG. 1B represents more particularly, the arrangement of the prior art that is implemented in a classical LTE (or WiMAX) receiver using two antennas (Rx0 and Rx1). In this embodiment of the prior art, each carrier (carrier 1 and carrier 2) is processed by both antennas chain (Rx1 and Rx2). For each antenna and each carrier, the first to fourth modules are implemented. In the embodiment of the prior art represented by FIG. 1B two fifth modules (151, 152) comprising an equalizer, and two sixth modules (161, 162) comprising a turbo decoder are implemented to process all the data of carrier 1 received by both Rx0 and Rx1 on the one hand (151, 161), and on the other hand all the data of carrier 2 received by both Rx0 and Rx1 (152, 162).
Carrier 1 and carrier 2 of FIG. 1B related to the prior art are then aggregated in the MAC layer level 17.
FIG. 1C is a detailed representation of two alternative embodiments (1000 and 1010) of the “front end” part of the classical and basic arrangement of the prior art for receiving an OFDM signal (one with a phase ramp multiplier 1400, the other with a numerically control oscillator 1210).
According to the first alternative 1000, the second module 120 comprises a front end filter, used to remove all the interference adjacent to the channel and a complex rotator, which compensates for the residual frequency offset, and the fourth module 140 comprises a phase ramp multiplier 1400, which compensates for the residual timing period offset in addition to the channel estimation means.
According to the second alternative 1010, the second module 1200 comprises a numerically controlled oscillator 1210 in addition to the front end filter and the complex rotator, which compensates for the residual frequency offset and/or the timing period offset, and the fourth module 14 comprises only the channel estimation means.
As illustrated by FIGS. 1A to 1C, according to the classic and basic arrangement for carrier aggregation, the aggregation is indeed then performed on the decoded data delivered by the front end at the MAC layer level 17.
As a result, considering the basic arrangement, the bandwidth corresponding to each channel is managed independently and separately using classical PHY layers arrangement, and the carriers of each channel are aggregated at the MAC layer level, i.e. the aggregation point is located in the MAC layer.
According to the release 10 of LTE, several scenarios of carrier aggregation can be implemented in order to permit the User Equipment (UE) to transmit and receive on several wireless channels simultaneously instead of using a single channel.
Several examples of scenarios are illustrated in the FIG. 2. Those examples are generic and applied to carrier aggregation in general.
Thus, for example in the first scenario 21, the user equipment uses two contiguous channels of the same bandwidth (e.g. 20 MHz) to sustain a maximum throughput as if it would be using a single 40 MHz channel.
In the second scenario 22, the user equipment uses two channels that are non contiguous but of same bandwidth.
In the third scenario 23, the mobile uses two channels that are non contiguous and of different bandwidths (BW) (e.g. 20 MHz and 5 MHz).
Another scenario (not represented) could consist in that the user equipment uses more than two channels (e.g. 20 MHz, 15 MHz and 5 MHz).
In addition, LTE defines several categories to specify the capability of performing carrier aggregation for a user equipment, which corresponds to the number of carriers that can be aggregated as well as the maximum aggregated bandwidth (defined in resource blocks (RB) which is a group of 12 carriers). These categories are summarized in the table below:
Carrier AggregationAggregated TransmissionNumber ofBandwidth ClassBW Configuration (in RB)aggregated carriersA≦1001B≦1002C100-2002
Some other classes D, E and F exist also and include more component carriers and possibly more than 200 aggregated RBs.
Thus, considering that various scenarios or carrier aggregation bandwidth class can be implemented, changing of scenario or even of carrier aggregation bandwidth class involves the change or adaptation of all the modules comprised in the front end of the PHY layers of the basic arrangement.
2. Prior Art Drawbacks
Thus a first disadvantage of the basic arrangement is its lack of “reconfigurability”. This basic arrangement results indeed in dramatically multiplying the changes of every modules of the “front end” part of the chain in order to adapt to a change of scenario.
In addition, the basic arrangement involves a sufficient die size to support as many modules as it is required by the different scenarios or the different carrier aggregation bandwidth classes, which is not in line when considering that future user equipments always aim at saving area.
Another disadvantage of the basic arrangement is its cost: to support all the scenarios as described above, each module shall be dimensioned to support the worst scenario per carrier.
Moreover, it appears also that managing independently each channels using several independent PHY layers, is not even efficient in terms of power consumption. Indeed, the power consumption of all the PHY layers corresponds to the power consumption of one PHY layer times the number of channels. And in addition, the change of scenario leads to a new power consumption, which often involves great power consumption variations.